Bilateral conjugacy of movement initiation is retained at the eye but not at the mouth following long-term unilateral facial nerve palsy

Laterality of proprioception in the orofacial muscles and temporomandibular joint

Laterality of function in the orofacial musculature suggests there may be side-to-side asymmetry of proprioceptive acuity in lip movement compared to the temporomandibular joint (TMJ). In the present work, 14 young adults were tested for acuity of lip and TMJ closure movements onto plugs varying from 5 to 8mm without visual feedback. Testing was conducted on both left and right sides, using the same psychophysical task and stimuli. Results showed superior proprioceptive acuity at the lips, with no significant side effect. However, there was side-to-side asymmetry in the correlations between proprioceptive performance for the two anatomical structures, with performance on the right side strongly correlated but not on the left. This is consistent with the need for coordination between structures during chewing. When acuity at different points in the stimulus range was examined, the right side lips were better with small stimuli. Overall, results support enhanced use-specific proprioception.

Proprioceptive ability at the lips and jaw measured using the same psychophysical discrimination task

In the human face, the muscles and joints that generate movement have different properties. Whereas the jaw is a conventional condyle joint, the facial musculature has neither distinct origin nor insertion points, and the muscles do not contain muscle spindle proprioceptors. This current study aims to compare the proprioceptive ability at the orofacial muscles with that of the temporomandibular joint (TMJ) in 21 neuro-typical people aged between 18 and 65 years. A novel psychophysical task was devised for use with both structures that involved a fixed 30.5 mm start separation followed by closure onto stimuli of 5, 6, 7, 8 mm diameter. The mean proprioceptive score when using the lips was 0.84 compared to 0.79 at the jaw (p < 0.001), and response error was lower by 0.1 mm. The greater accuracy in discrimination of lip movement is significant because, unlike the muscles controlling the TMJ, the orbicularis oris muscle controlling the lips inserts on to connective tissue and other muscle, and contains no muscle spindles, implying a different more effective, proprioceptive mechanism. Additionally, unlike the lack of correlation previously observed between joints in the upper and lower limbs, at the face the scores from performing the task with the two different structures were significantly correlated (r = 0.5, p = 0.018). These data extend the understanding of proprioception being correlated for the same left and right joints and correlated within the same structure (e.g. ankle dorsiflexion and inversion), to include use-dependant proprioception, with performance in different structures being correlated through extended coordinated use. At the lips and jaw, it is likely that this arises from extensive coordinated use. This informs clinical assessment and suggests a potential for coordinated post-injury training of the lips and jaw, as well as having the potential to predict premorbid function via measurement of the uninjured structure, when monitoring progress and setting clinical rehabilitation goals.

A series of 3 cases of corneal abrasion with multiple etiologies

BACKGROUND

Most corneal abrasions are caused by mechanical injuries affecting the superficial epithelial layer. Although one of the functions of the eyelid is to protect the eye, its reaction time of about 425 msec is slower than many ocular insults; thus, corneal abrasions are among the most commonly occurring eye emergencies.

CASE REPORTS

Three cases of corneal abrasions with different etiologies are presented. The first case was a large abrasion of the cornea near the visual axis caused by a wood chip. A metal foreign body with rust was lodged in the cornea from metal grinding in the second case. The third case was iatrongenically induced by an A-scan probe while a fellow student was measuring the axial length of the eye.

CONCLUSION

Corneal abrasions are one of the most common ocular conditions presented to eye clinics or emergency departments. Although there are different etiologies of abraded corneal epithelium, current clinical management for most corneal abrasions involves a bandage contact lens, use of topical antibiotics, and cycloplegics. Large and central corneal abrasions, however, warrant a consultation with a corneal specialist.